Cleaning oxides from steel



' Patented June 19, 1945 CLEANING OXIDES FROM STEEL Frank Forsberg, Worcester, Mass., assignor to The American Steel and Wire Company of New Jersey, a corporation of New Jersey Application October 17, 1941, Serial No. 415,467

3 Claims.

This invention is a, method of electrolytically cleaning oxidized steel.

According to the method, the oxidized steel is immersed in molten sodium nitrate, the electric current being passed through this salt to the steel so as to dissociate the former and thus deposit sodium on the latter. It is'to be understood that the direction of the current is considered to be from positive to negative whereby the steel will be the cathode. The sodium nitrate dissociates and deposits sodium on the steel, this sodium'reacting with the oxide on the steel so that it is oxidized to sodium peroxide.

When the steel is thus cleaned it may be removed from the salt. Since it will be coated with sodium peroxide there is no danger of it again becoming oxidized. The removal of this peroxide coating may be easily effected by rinsing the steel. The rinsing may also function to cool the steel to a point where there is no danger of oxidation, it being obvious that the removal of the sodium peroxide coating leavesits surfaces unprotected. The steel may then be immersed in cold acid to neutralize any sodium peroxide which might not have been removed by the rinsing. That is to say, the acid used is not heated to temperatures common to ordinary pickling optively simple proposition. It is to be understood that the fused salt may be contained in a conventional steel kettle.

In order to lower the temperature required to maintain the sodium nitrate molten, a mixture of about 80% of this salt and about 20% of potassium nitrate may be used. This enables the use of temperatures of from 700 to 1000 degrees F. and provides for the usual economies connected with the use of lower temperatures. However,. the sodium salt is to be considered as the active agentin the electrolytic cleaning.

eratlons since this would cause the steel to absorb hydrogen and become subject to acid brittleness. 1

A specific example of a method embodying the l foregoing principles will now be disclosed with which it exits at temperatures sufliciently high to cause its surface to absorb'oxygen from the atmosphere. 4

Leaving the lead annealer, the-wire enters the bath of fused salt where the electrolytic cleaning is to take place. According to the invention, this salt is sodium nitrate which deposits sodium on .the wire when a. current is passed through it to the latter. The use of this salt involves a further advantage in that evolutions of nitrogenoxides take place at the surface of the steel kettle which is the anode. This prevents sludges from sticking to the surface of the steel kettle and The voltages used may range from 6 to 12 volts, 10 volts being considered preferable. The time the wire requires to pass through the salt may vary from 30 to 90 seconds, depending on its state of oxidation.

Oxides on the surface of the wire are removed by the sodium reacting to form sodium peroxide. The oxygen of the atmosphere is prevented from combining with the sodium by the fact that the entire reaction takes place beneath the level of the fused salt,

When the wire leaves the electrolytic cleaner it carries a coating of sodium peroxide which prevents its surface from becoming oxidized or blued, it being understood that this might otherwise occur because of the elevated temperature of the wire resulting from its passage through the molten salt. This coating is removed by the passage of the wire through a water rinse which at the same time lowers the temperature of the wire to a point whereoxidation need no longer be feared.

From the water rinse the wire goes through a bath of cold, hydrochloric acid. Since this acid is cold or at least at no greater than room temperature, there is no danger of it imparting acid brittleness to the wire. The only function of this acid is to neutralize any of the basic sodium peroxide which might accidentally remain on the wire after its passage through the water rinse. From the hydrochloric acid bath the wire passes through another water rinse where the acid is removed, and from there it goes on to other processing equipment for galvanizing, tinning, or

other operations.

Although the specific example of the invention is in connection with steel in the form of wire, it is to be understood that the invention is equally applicable to the cleaning of sheets and other forms of steel.

Furthermore, although the sodium salt is to be considered as the active agent in the electromakes cleaning of its bottom byscraplng a relalytlc cleaning, the potassium salt effectively protrolytic action at the surface of the steel kettle. so as to form nitrogen-oxide evolutions. At the same time, this desired eiiect is critically greater in the case of sodium nitrate. Also, sodium nitrate has the further great advantage that it is much more available and, hence, inexpensive than other usable compounds.- 1

This application is a continuation inpart of in a bath including molten sodium compound, the method comprising the 'use of ferrous kettle for the bath and the inclusion or sodium nitrate by the bath in conjunction with pas the current from the kettle throush the bath to the metal'being treated in the latter, whereby the kettle is the anode, the current causing evolutions of nitrogen-oxides at the surfaces of the kettle contacted by the bath, to prevent sludges 10 from sticking to these surfaces and making cleaning or these surfaces by scraping a relatively simple proposition, the bath consisting mainly of sodium nitrate and sumcient potassium nitrate an application filed July 30, 1936, Serial No.

I claim:

1. In the art of electrolytically treating metal in a bath including molten sodium compound, the method comprisingthe use of a ferrous kettle for the bath and the inclusion of sodium nitrate by the bath in conjunction with passing the current from the kettle through the bath to the metal being treated in the latter, whereby the kettle is the anode, the current causing evolutions of nitrogen-oxides at the surfaces of the kettle contacted by the bath, to prevent sludges from sticking to these surfaces and making clean- *ing of these surfaces by scraping a relatively simple proposition.

2. In the art of electrolytically treating metal to lower the fusing temperature-oi the bath-to a degree permitting economical operation.

3. In the art 0! electrolytically treating metal in abath including molten sodium compound, the method comprising the use of a ferrous kettle for the bath and the inclusion or a nitrogen I and oxygen containing compound by the bath having the characteristic of evolving nitrogenoxides at the anodewhen in an electrolytic circult, in conjunction with passing the current from the kettle through the bath to the metal being treated in the latter, whereby the kettle is the anode, the current causing evolutions of nitrogen-oxides at the surfaces of the kettle contacted by the bath, to prevent sludges from sticking to thesesurfaces and making cleaning 01' these surfaces by scraping a relatively simple proposition. FRANK EDRSBERG. 

